Slurry hydroconversion with pitch recycle

ABSTRACT

Systems and methods are provided for performing slurry hydroconversion of feeds that include substantial amounts of 1050° F+ (566° C+) components. The productivity of the slurry hydroconversion reaction is improved by recycling slurry hydroconversion pitch or bottoms back to the slurry hydroprocessing reaction system. The mass flow rate of the recycle stream can correspond to 50% or more of the mass flow rate of the fresh feed to the reaction system, and the recycle stream can include more than 50 wt % of 566° C+ components. It has been discovered that using a substantial recycle stream composed of a majority of unconverted 566° C+ bottoms can increase the productivity of the slurry hydroprocessing reaction system when operating at a net conversion relative to 524° C (975° F) of less than 90 wt %. Additionally, by using a recycle stream composed of a majority of 566° C+ components, the amount of lower boiling components (in the heavy hydrocarbon feed and/or in the recycle stream) that are exposed multiple times to the slurry hydroprocessing environment is reduced or minimized This can allow for formation of slurry hydroconversion products with increased amounts of vacuum gas oil boiling range components.

FIELD OF THE INVENTION

Systems and methods are provided for performing slurry hydroconversionof heavy oil feeds with recycle of the pitch or hydroconversion bottoms.

BACKGROUND OF THE INVENTION

Developing effective methods for processing and/or disposition of feedsincluding substantial amounts of 1050° F+ (566° C+) components is anongoing challenge. Such heavy hydrocarbon feeds can have a relativelylow value without processing, as the value of such feeds for use inasphalt or fuel oil is limited. Unfortunately, such heavy hydrocarbonfeeds also have a tendency to cause fouling or other degradation inprocessing equipment. As a result, attempting to process such heavyhydrocarbon feeds can require substantial equipment investment inaddition to resource investments for reagents and solvents used toprocess the feeds.

Various types of coking are examples of common methods for processing ofheavy hydrocarbon feeds. Coking can be effective for processing of awide variety of types of heavy hydrocarbon feeds without requiringexcessive equipment costs and/or excessive use of additional resources.However, as the boiling range of a feed increases, the hydrogen contentof heavy hydrocarbon feed tends to be reduced, leading to increasingamounts of coke production for heavier feeds. Such coke productionlimits total liquid yields and can further constrain the types of liquidproducts generated. For example, for feeds including substantial amountsof 566° C+ components, the coke yields can correspond to 30 wt % or moreof the feedstock. When coking is used at remote geographic location,this substantial coke production can pose additional difficulties, asoutlets for sale and/or disposal of the coke may be limited.

Coke production also contributes to the difficulties when attempting tohydroprocess feedstocks with substantial contents of 566° C+ components.Although hydroprocessing typically results in lower coke formation thancoking, such coke formation can still lead to rapid fouling and/ordegradation of hydroprocessing equipment, including hydroprocessingcatalyst. As a result, mitigation of coke formation is a primary concernwhen attempting to hydroprocess a feed with a substantial content of566° C+ components.

Some conventional methods for hydroprocessing of heavy feeds havefocused on strategies related to using a solvent and/or recycle streamto reduce the relative amount of 566° C+ components present in thereaction environment. Conventionally, it is believed that reducing theamount of 566° C+ components in the reaction environment can reduce orminimize coke formation. Thus, in such strategies, the solvent orrecycle stream includes a majority of components that boil below 566° C.This assists with maintaining a lower relative content of 566° C+components in the reaction environment. However, this also leads toadditional conversion of the recycle stream to lower boiling, lowervalue products. Additionally, for slurry hydroprocessing reactors, it isconventionally believed that bottoms recycle leads to reduced reactorproductivity.

U.S. Pat. No. 5,972,202 describes an example of this strategy forreducing the relative amount of high boiling components in the reactionenvironment. In U.S. Pat. No. 5,972,202, slurry hydrocracking isperformed using a recycle stream corresponding to 65 wt % or less of thefresh feed to the slurry hydrocracking stage. The recycle streamincludes a small amount of 524° C+ material as part of a pitch fraction,while the majority of the recycle stream corresponds to vacuum gas oilboiling range stream described as an aromatic oil. The recycle of thearomatic oil is described as preventing the accumulation of asphalteneson additive particles in the slurry hydroprocessing environment.

U.S. Pat. No. 6,004,453 describes a similar strategy for performingslurry hydrocracking with a recycle stream comprising a majority ofvacuum gas oil boiling range components. It is noted that having amajority of the recycle stream correspond to vacuum gas oil boilingrange components is described as being necessary for inclusion of pitchin the recycle stream, in order to prevent coke formation.

U.S. Pat. No. 4,252,634 describes slurry hydroprocessing of a full rangebitumen where the volume of the recycle stream is at least twice thevolume of the fresh feed delivered to the reactor. The amount ofdistillate and/or gas oil in the recycle stream is greater than 50 wt %,with the pitch in the recycle stream being defined based on cut point of524° C. Thus, the portion of 566° C+ components in the recycle issubstantially below 50 wt %. The substantial recycle is described asbeing useful for preventing coke formation.

U.S. Pat. No. 8,435,400 provides an example of why conventional recyclemethods have focused on recycle of lower boiling range portions. In U.S.Pat. No. 8,435,400 slurry hydroprocessing of vacuum resid boiling rangefeeds is performed in a multi-stage reaction system. Some examplesdescribe performing slurry hydroprocessing with recycle of a bottoms orresid stream from the final stage to an earlier stage, as opposed tohaving a recycle stream including a majority of lower boilingcomponents. The recycle stream corresponded to roughly 15 wt % of thefresh feed into the reaction system. In the examples, it was reportedthat operating with recycle required a significantly higher catalystconcentration than once-through operation in order to maintain the samelevel of feed conversion at a given temperature. Operating with recycleat this increased catalyst concentration appeared to provide no benefitor improvement for the productivity of the reaction system.

U.S. Pat. No. 5,374,348 describes another example of conventionalrecycle during slurry hydrocracking of feed. A feed including a 524° C+portion is processed in a slurry hydrocracking environment in thepresence of additive (catalyst) particles. The hydrocracked effluent isfractionated to form a 450° C+ fraction that also includes a substantialportion of the additive particles. Up to 40 wt % of the 450° C+ fraction(relative to the weight of fresh feed) is recycled to the slurryhydroconversion reactor. The recycle stream allowed for a reduction inthe amount of additive particles required for performing the slurryhydrocracking. Based on the examples, it appears that the reactorproductivity after addition of the recycle stream was similar orslightly decreased relative to operating without the recycle stream.

In other types of hydroprocessing environments, use of bottoms recyclewould be expected to either reduce reactor productivity or have noimpact. U.S. Pat. No. 4,983,273 describes a fixed bed hydrocrackingprocess for use with various feeds. The reaction system includes ahydrotreatment stage and a hydrocracking stage. A series of examples ofhydrocracking of a vacuum gas oil boiling range feed are provided. Inexamples where bottoms recycle is used to return unconverted feed to thehydrotreatment stage, a decrease in reactor productivity for thehydrotreatment stage was observed. In examples where bottoms recycle wasused to return unconverted feed to the hydrocracking stage, reactorproductivity was substantially not changed, but the yield of distillateboiling range products was increased at the expense of naphtha productsand light ends products. An improvement in denitrogenation with recycleto the hydrocracking reactor was also reported.

The other conventional strategy for mitigating coke formation is relatedto removal of asphaltenes from a recycle stream prior to introducing therecycle stream back into a reactor. Conventionally, it is believed thatone of the sources of coke formation is due to loss of ability tomaintain asphaltenes in solution in a heavy feedstock. By removingasphaltenes from the processing environment, this incompatibility issueis removed, and therefore coke formation in the reaction environment canbe reduced or minimized While removal of asphaltenes can be effective,the asphaltene content can correspond to 15 wt % or more of the 566° C+portion of a feed. Thus, removal of asphaltenes from a recycle streamrepresents a substantial loss of carbon to low (or possible zero) valueproducts before considering any other losses due to hydroprocessing.

U.S. Pat. No. 9,982,203 provides an example of this type of strategy,where an ebullating bed reactor is used to hydroconvert an atmosphericresid or vacuum resid feed. In some configurations, a recycle stream isreturned to the reactor that is formed by deasphalting thehydroconversion bottoms to form deasphalted oil. By definition, adeasphalted oil recycle stream contains a minimized amount ofasphaltenes. It is noted that this type of configuration would presentadditional challenges when attempting to use slurry hydroprocessing, asany catalyst in the hydroconversion bottoms would preferentially beseparated into the deasphalter rock, and not the deasphalted oil.

U.S. Pat. No. 4,411,768 describes another example of asphaltene removal.In U.S. Pat. No. 4,411,768, removal of coke precursors is described asenabling higher conversion rates while avoiding reactor fouling. Anebullating bed reactor with a bottoms recycle loop is used forhydroconversion of a heavy feed. Prior to recycle of the hydroconversionbottoms, the bottoms are chilled to a temperature that causesprecipitation and/or separation of all toluene insolubles and n-heptaneinsolubles (i.e., asphaltenes) in the recycle stream. As noted above,this represents a substantial rejection of material, as the n-heptaneinsolubles can correspond to 15 wt % or more of the 566° C+ portion of afeed, and the toluene insolubles can correspond to an additional 5 wt %or more of the 566° C+ portion of a feed.

U.S. Pat. No. 4,808,289 is directed to a method for performinghydroconversion in an ebullating bed unit while avoiding the need toremove coke precursors (such as asphaltenes) from any recycle streams.The solution provided in U.S. Pat. No. 4,808,289 is to perform a limitedamount of recycle of flash drum bottoms, where the recycle streamincludes at least 50 vol % gas oil boiling range components. In otherwords, the need to remove asphaltenes is avoided by using the firststrategy described above, so that the recycle stream includes 50 vol %or more of lower boiling components.

What is needed are systems and methods that can allow forhydroconversion of heavy feeds that can mitigate reactor fouling whileminimizing loss of reactor productivity and also minimizing losses ofportions of a feed to lower value products, including reducing orminimizing overcracking.

SUMMARY

In various aspects, a method for performing slurry hydroconversion isprovided. The method includes exposing a heavy hydrocarbon feed and apitch recycle stream to a slurry hydroprocessing catalyst under slurryhydroconversion conditions in a reaction zone to form a slurryhydroprocessing effluent. The slurry hydroconversion conditions caninclude a net conversion of 60 wt % to 89 wt % relative to 524° C. Theheavy hydrocarbon feed can include 50 wt % or more of 566° C+components. Optionally, the heavy hydrocarbon feed and the pitch recyclestream can have a combined feed ratio of 1.5 to 3.5. The method canfurther include separating the pitch recycle stream from the slurryhydroconversion effluent. The pitch recycle stream can include more than50 wt % of 566° C+ components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a reaction system configuration for slurryhydroprocessing.

FIG. 2 shows comparative results from fixed bed hydroprocessing of avacuum resid feedstock.

FIG. 3 shows product yield slates from slurry hydrocracking with variouslevels of pitch recycle at constant 566° C+ conversion.

FIG. 4 shows product yield slates from slurry hydrocracking with variousamounts of 566° C+ material in a pitch recycle stream at constant 566°C+ conversion.

DETAILED DESCRIPTION

All numerical values within the detailed description and the claimsherein are modified by “about” or “approximately” the indicated value,and take into account experimental error and variations that would beexpected by a person having ordinary skill in the art.

Overview

In various aspects, systems and methods are provided for performingslurry hydroconversion of feeds that include substantial amounts of1050° F+ (566° C+) components. The productivity of the slurryhydroconversion reaction is improved by recycling slurry hydroconversionpitch or bottoms back to the slurry hydroprocessing reaction system. Themass flow rate of the recycle stream can correspond to 50% or more ofthe mass flow rate of the fresh feed to the reaction system, and therecycle stream can include more than 50 wt % of 566° C+ components. Ithas been discovered that using a substantial recycle stream composed ofa majority of unconverted 566° C+ bottoms can increase the productivityof the slurry hydroprocessing reaction system when operating at a netconversion relative to 524° C (975° F) of less than 90 wt %. Forexample, the net conversion can be 50 wt % to 89 wt % relative to 524°C, or 60 wt % to 89 wt %, or 70 wt % to 89 wt %. Additionally, by usinga recycle stream composed of a majority of 566° C+ components, theamount of lower boiling components (in the heavy hydrocarbon feed and/orin the recycle stream) that are exposed multiple times to the slurryhydroprocessing environment is reduced or minimized This can allow forformation of slurry hydroconversion products with increased amounts ofvacuum gas oil boiling range components.

Slurry hydroconversion is a hydroprocessing method that can achieve highconversion of heavy hydrocarbon feeds to liquid hydrocarbons withoutrejecting carbon. Conventionally, slurry hydroconversion has had onlylimited use, due in part to difficulties in balancing the high pressureand/or high liquid residence time required to achieve high conversionwhile avoiding reaction conditions that result in either foaming orfouling in the reactor.

A slurry hydroprocessing reactor operates as a bubble column, so thatboth gas and liquid are present within the reactor volume duringoperation. This creates a tension during operation when managing the gassuperficial velocity and the liquid superficial velocity in the reactor.If the gas superficial velocity becomes too high relative to the liquidsuperficial velocity, the liquid phase in the reactor can begin to foam,which quickly leads to an inability to operate effectively.Unfortunately, reducing the gas superficial velocity by reducing therate of introduction of hydrogen treat gas leads to lower partialpressures of hydrogen, which can result in increased coke formation.Additionally, increasing the liquid superficial velocity by increasingthe fresh feed rate, at constant temperature, typically results inreduced conversion.

One option for increasing the liquid superficial velocity withoutrequiring an increase in the fresh feed rate is to recirculate a portionof the total liquid effluent back to the reactor. This can beaccomplished using a pump-around recirculation loop. In this discussion,recirculation of liquid effluent portion to a reactor is defined asreturning to the reactor a portion of liquid effluent that hassubstantially the same composition as the liquid within the reactor. Inother words, the liquid effluent is not fractionated and/or chemicallymodified prior to returning the liquid effluent to the reactor.Recirculation of liquid effluent can improve the hydrodynamics ofoperation within a slurry hydroprocessing reactor. Such recirculationcan reduce or minimize the potential for “foaming” in the slurryhydroconversion environment. When determining “per pass” conversionwithin the reactor, the reactor is defined to include any recirculationloops. Thus, liquid within a recirculation loop, by definition, isliquid that remains in the reactor. Any conversion performed on liquidthat has traveled through a recirculation loop is therefore consideredpart of the “per pass” conversion.

In contrast to recirculation, recycle of liquid to the slurryhydroconversion reactor corresponds to recycle of a liquid fraction thathas a different composition than the liquid phase in the reactor.Conventionally, however, recycle of the bottoms from a hydroconversionreaction is believed to not be beneficial when processing a heavyfeedstock in a slurry hydroprocessing reaction environment. This is duein part to lowering of reactor productivity when using recycle streamsthat are small relative to the rate of fresh feed in the reactor. Whenusing these relatively small recycle amounts, incorporation of asubstantial amount of bottoms in the recycle can lead to increasedcoking. In order to avoid this coking, the temperature needs to belowered to avoid reactor fouling, but this also requires a correspondingdecrease in fresh feed rate in order to maintain a constant level offeed conversion. In order to avoid this choice between increased reactorfouling and decreased reactor productivity, conventional recycle streamsfor slurry hydrocracking units have focused on use of streams where 50wt % or more of the recycle stream corresponds to vacuum gas oil boilingcomponents (and/or other lower boiling range components).

In contrast to the above, it has been discovered that when performingconversion of a sufficiently heavy feedstock, such as a heavyhydrocarbon feedstock including more than 50 wt % of 566° C+ components,or more than 50 wt % of 593° C+ components, an unexpected productivityincrease can be achieved by operating a slurry hydroprocessing reactor(or reaction system) with a substantial recycle of pitch or unconvertedbottoms, so long as the recycle stream is also sufficiently heavy. Thesubstantial recycle can correspond to a recycle stream having a massflow rate corresponding to 50% or more of the mass flow rate of freshfeed delivered to the reaction system, such as 50% to 250% of the amountof fresh feed, or 50% to 200%, or 60% to 250%, or 60% to 200%. Suchrecycle rates correspond to a combined feed ratio of 1.5 to 3.5, or 1.5to 3.0, or 1.6 to 3.5, or 1.6 to 3.0. Additionally, the substantialrecycle can correspond to a pitch or unconverted bottoms stream thatincludes more than 50 wt % of 566° C+ components, or 60 wt % or more.Optionally, the substantial recycle can correspond to a pitch orunconverted bottoms stream that includes 50 wt % or more of 593° C+components, or 60 wt % or more.

It has been discovered that recycling pitch (unconverted slurryhydroconversion product) can significantly improve the economics of theslurry hydroconversion process when performing hydroconversion at netconversion levels of less than 90 wt % relative to 524° C. Inparticular, recycling pitch can unexpectedly improve reactorproductivity, allowing an increase in the unit capacity at constant 524°C net conversion. This is in contrast to conventional recycle methods,where using recycle streams containing 50 wt % or more of lower boilingcomponents results in loss of reactor productivity (i.e., the fresh feedrate is reduced at constant net conversion at constant temperature). Forexample, when operating slurry hydroconversion with pitch recycle, theamount of net conversion relative to 524° C can be 60 wt % to 89 wt %,or 70 wt % to 89 wt %, or 60 wt % to 85 wt %, or 70 wt % to 85 wt %, or75 wt % to 89 wt %. It is noted that the conversion at 566° C will behigher than the conversion at 524° C. The per-pass conversion can belower, corresponding to 60 wt % or less conversion relative to 524° C.

Without being bound by any particular theory, it is believed that usinga sufficiently high amount of a sufficiently heavy recycle can reducethe formation of incompatible compounds in the reactor environment. Itis believed that the formation of incompatible compounds is reduced orminimized in part by reducing exposure of lower boiling components tothe reaction environment multiple times, and in part by reducing theseverity (i.e., reducing the per-pass conversion) of the reactionenvironment.

Under conventional conditions for slurry hydroconversion of 60 wt % ormore of a feedstock relative to 524° C, the fresh feed into the reactionenvironment can often contain a substantial portion of lower boilingcompounds, such as vacuum gas oil boiling range components (343° C-566°C components). It is believed that additional (secondary) cracking ofsuch vacuum gas oil boiling range compounds increases the likelihood ofresid (566° C+) components becoming incompatible with the liquid phasein the reaction environment. It is further believed that the amount ofincompatible compounds generated due to overcracking of vacuum gas oilboiling range compounds within the slurry hydroprocessing reactionenvironment increases with increasing conversion relative to 524° C. Itis believed that by increasing the amount of 566° C+ compounds in thereaction environment, and operating at moderate per-pass conversion, theproblems due to incompatibility can be reduced or minimized This allowsthe reactor to be operated at increased productivity while maintainingreduced or minimized coke formation.

Due to the above combination of factors, using small recycle streams(regardless of composition) can tend to reduce the productivity of aslurry hydroprocessing reactor, or at best lead to no change inreactivity. When using a small recycle stream containing less than 40 wt% of the amount of fresh feed, at constant net conversion, the change insingle-pass conversion in the reactor can be relatively small. As aresult, introducing a small recycle stream does not provide asubstantial reduction in the severity of the reaction environment.However, such small recycle streams typically also include previouslyprocessed vacuum gas oil boiling range components, which are thenintroduced into the reaction environment. It is believed that thesepreviously processed vacuum gas oil boiling range components have anincreased tendency to form incompatible compounds at a given level ofconversion (or reaction condition severity). As a result, at constantfresh feed rate, the introduction of a small recycle stream is believedto result in either no impact on formation of incompatible compounds oran increase in formation of incompatible compounds. Thus, in order toavoid fouling, when using small recycle streams, the flow of fresh feedis reduced and/or large excesses of lower boiling components areincluded in the recycle stream.

By contrast, it has been discovered that using a substantially largerrecycle stream, with a sufficiently large content of 566° C+ components,can provide increased reactor productivity when operating at netconversions of 60 wt % to less than 90 wt % for slurry hydroconversionof a heavy hydrocarbon feed. Without being bound by any particulartheory, it is believed that the productivity benefits are based on acombination of factors that allow for operation of a slurryhydroprocessing reactor in an unexpected region of the reactioncondition phase space for slurry hydroconversion. First, using asufficiently high boiling initial feed, such as a heavy hydrocarbon feedcontaining 50 wt % or more of 566° C+ components, reduces or minimizesthe amount of fresh feed that is susceptible to formation ofincompatible compounds during a single pass through the slurryhydroconversion reactor. Second, using a recycle stream corresponding to50 wt % or more of the fresh feed provides a sufficient amount ofrecycle so that the per-pass conversion can be substantially reduced.For example, by using a sufficient amount of recycle, the per-passconversion relative to 524° C can be lower than the net conversionrelative to 524° C by 15% or more, or 25% or more, or 30% or more, suchas having a per-pass conversion that is lower than the net conversion byup to 50% or possibly still higher. By reducing the per-pass conversion(i.e., reducing the severity in the reactor), the amount of incompatiblecompounds generated in the reaction environment can be reduced. Third,by using a recycle stream containing more than 50 wt % of 1050° F+ (566°C+) components, the amount of previously processed lower boilingcomponents introduced into the slurry hydroprocessing reactionenvironment can be reduced. This can further reduce or minimizegeneration of incompatible compounds within the reaction environment.

Based on the above factors, performing substantial recycle using asufficiently heavy recycle stream allows for reduced formation ofincompatible compounds. This reduction in formation of incompatiblecompounds allows the reaction system to process an unexpectedly heavycombination of feed and recycle streams while avoiding fouling and/orshutdown of the reactor due to substantial coke formation. By enablingoperation in an unexpected region of the slurry hydroconversion phasespace, additional benefits are also achieved. For example, by operatingwith a recycle stream containing a sufficiently high content of 566° C+components, reactor productivity is increased, as an increasedpercentage of the reactions within the reaction environment correspondto primary cracking of 566° C+ compounds, as opposed to secondarycracking of 566° C− compounds. Such secondary cracking of 566° C−compounds is further reduced or minimized based on the lower single-passconversion.

It is noted that the absence of any one of the multiple factorsdescribed above can inhibit or prevent the ability to access theunexpectedly desirable region of the reaction condition phase space forslurry hydroconversion. For example, if the size of the recycle streamis not sufficiently large, the reduction in per-pass conversion will notbe sufficient to realize the benefits of the recycle, and instead adecrease in productivity will be observed. If the initial feedstockand/or the recycle stream does not contain a sufficiently high contentof 566° C+ material, the feed itself will contain an undesirable amountof vacuum gas oil boiling range compounds that are susceptible toovercracking to form incompatible compounds.

In addition to improving reactor productivity, operating a slurryhydroprocessing reactor with pitch recycle can potentially providevarious additional benefits. For example, bottoms or pitch recycle canincrease the catalyst concentration in the reactor, permitting areduction in the catalyst make-up rate and/or higher severity operation.

Still other potential benefits can include, but are not limited to:reducing or minimizing the amount of secondary cracking of primary VGOproducts into incompatible paraffin side chains and aromatic cores;improving VGO quality to facilitate processing in downstream units;and/or reducing hydrogen consumption and light ends production.

Definitions

In this discussion, unless otherwise specified, “conversion” of afeedstock or other input stream is defined as conversion relative to aconversion temperature of 524° C (975° F). Per-pass conversion refers tothe amount of conversion that occurs during a single pass through areactor/stage/reaction system. It is noted that recirculation streams(i.e., streams having substantially the same composition as the liquidin the reactor) are considered as part of the reactor, and therefore areincluded in the calculation of per-pass conversion. Net or overallconversion refers to the net products from the reactor/stage/reactionsystem, so that any recycle streams are included in the calculation ofthe net or overall conversion. It is noted that in all aspects describedherein, the amount of conversion at 524° C is lower than thecorresponding conversion at 566° C.

In this discussion, the productivity of a reactor/reaction system isdefined based on the feed rate of fresh feed to the reactor/reactionsystem that is required in order to maintain a target level of netconversion relative to 524° C at constant temperature. An increase infresh feed rate while maintaining net conversion at constant temperaturecorresponds to an increase in productivity for a reactor/reactionsystem.

In this discussion, primary cracking is defined as cracking of 566° C+components in the feed. Secondary cracking refers to any cracking of566° C− components.

In this discussion, gas holdup refers to the amount of gas presentwithin the reactor at a given moment in time.

In this discussion, the “combined feed ratio” (or CFR) is defined as aratio corresponding to (mass flow rate of fresh feed+mass flow rate ofrecycle stream)/(mass flow rate of fresh feed). Based on thisdefinition, the combined feed ratio when no recycle is used is 1.0. Whenrecycle is present, the relative mass flow rate of the recycle stream asa percentage of the fresh feed can be added to 1.0 to provide thecombined feed ratio. Thus, when the mass flow rate of the recycle streamis 10% of the mass flow rate of the fresh feed, the CFR is 1.1. When themass flow rate of the recycle stream is 50% of the mass flow rate of thefresh feed, the CFR is 1.5. When the mass flow rate of the recyclestream is 100% of the mass flow rate of the fresh feed, the CFR is 2.0.

In this discussion, when describing the amount of a fresh feed stream,recirculation stream, recycle stream, or other stream, the mass flowrate of the stream may also be referred to as a “weight” of the stream.

In this discussion, the Liquid Hourly Space Velocity (LHSV) for a feedor a portion of a feed to a slurry hydrocracking reactor is defined asthe volume of feed per hour relative to the volume of the reactor.

In this discussion, a “C_(x)” hydrocarbon refers to a hydrocarboncompound that includes “x” number of carbons in the compound. A streamcontaining “C_(x)—C_(y)” hydrocarbons refers to a stream composed of oneor more hydrocarbon compounds that includes at least “x” carbons and nomore than “y” carbons in the compound. It is noted that a streamcomprising C_(x)—C_(y) hydrocarbons may also include other types ofhydrocarbons, unless otherwise specified.

In this discussion, “Tx” refers to the temperature at which a weightfraction “x” of a sample can be boiled or distilled. For example, if 40wt % of a sample has a boiling point of 343° C or less, the sample canbe described as having a T40 distillation point of 343° C. In thisdiscussion, boiling points can be determined by a convenient methodbased on the boiling range of the sample. This can correspond to ASTMD2887, or for heavier samples ASTM D7169.

In this discussion, references to “fresh feed” to a hydroconversionstage correspond to feedstock that has not been previously passedthrough the hydroconversion stage. This is in contrast to recycled feedportions that are formed by fractionation and/or other separation of theproducts from the hydroconversion stage.

In various aspects of the invention, reference may be made to one ormore types of fractions generated during distillation of a petroleumfeedstock, intermediate product, and/or product. Such fractions mayinclude naphtha fractions, distillate fuel fractions, and vacuum gas oilfractions. Each of these types of fractions can be defined based on aboiling range, such as a boiling range that includes at least 90 wt % ofthe fraction, or at least 95 wt % of the fraction. For example, fornaphtha fractions, at least 90 wt % of the fraction, or at least 95 wt%, can have a boiling point in the range of 85° F (29° C) to 350° F(177° C). It is noted that 29° C roughly corresponds to the boilingpoint of isopentane, a C₅ hydrocarbon. For a distillate fuel fraction,at least 90 wt % of the fraction, or at least 95 wt %, can have aboiling point in the range of 350° F (177° C) to 650° F (343° C). For avacuum gas oil fraction, at least 90 wt % of the fraction, or at least95 wt %, can have a boiling point in the range of 650° F (343° C) to1050° F (566° C.). Fractions boiling below the naphtha range cansometimes be referred to as light ends. Fractions boiling above thevacuum gas oil range can be referred to as vacuum resid fractions orpitch fractions.

Another option for specifying various types of boiling ranges can bebased on a combination of T5 (or T10) and T95 (or T90) distillationpoints. For example, in some aspects, having at least 90 wt % of afraction boil in the naphtha boiling range can correspond to having a T5distillation point of 29° C or more and a T95 distillation point of 177°C or less. In some aspects, having at least 90 wt % of a fraction boilin the distillate boiling range can correspond to having a T5distillation point of 177° C or more and a T95 distillation point of343° C or less. In some aspects, having at least 90 wt % of a fractionboil in the vacuum gas oil range can correspond to having a T5distillation point of 343° C or more and a T95 distillation point of566° C or less.

In this discussion, the boiling range of components in a feed,intermediate product, and/or final product may alternatively bedescribed based on describing a weight percentage of components thatboil within a defined range. The defined range can correspond to a rangewith an upper bound, such as components that boil at less than 177° C(referred to as 177° C−); a range with a lower bound, such as componentsthat boil at greater than 566° C (referred to as 566° C+); or a rangewith both an upper bound and a lower bound, such as 343° C-566° C.

Feedstocks

In various aspects, the initial feed corresponds to a heavy hydrocarbonfeed. Examples of heavy hydrocarbon feeds include, but are not limitedto, heavy crude oils, distillation residues, oils (such as bitumen) fromoil sands, and heavy oils derived from coal. In this discussion, a heavyhydrocarbon feed corresponds to a feed where a substantial portion ofthe feed has a boiling point of 1050° F (566° C) or more, or 1100° F(593° C) or more. In some aspects, 50 wt % or more of a heavyhydrocarbon feed can have a boiling point of 566° C or more, or 60 wt %or more, or 70 wt % or more, or 80 wt % or more, such as up tosubstantially all of the heavy hydrocarbon feed corresponding tocomponents with a boiling point of 566° C or more. In some aspects, 50wt % or more of a heavy hydrocarbon feed can have a boiling point of593° C or more, or 60 wt % or more, or 70 wt % or more, or 80 wt % ormore, such as up to substantially all of the heavy hydrocarbon feedcorresponding to components with a boiling point of 593° C or more. Inthis discussion, boiling points can be determined by a convenientmethod, such as ASTM D2887, ASTM D7169, or another suitable standardmethod.

Density, or weight per volume, of the heavy hydrocarbon feed can bedetermined according to ASTM D287-92 (2006) Standard Test Method for APIGravity of Crude Petroleum and Petroleum Products (Hydrometer Method),and is provided in terms of API gravity. In general, the higher the APIgravity, the less dense the oil. API gravity can be 15° or less, or 10°or less, or 5° or less.

Heavy hydrocarbon feeds can be high in metals. For example, the heavyhydrocarbon feed can be high in total nickel, vanadium and ironcontents. In one embodiment, the heavy oil will contain at least 0.00005grams of Ni/V/Fe (50 ppm) or at least 0.0002 grams of Ni/V/Fe (200 ppm)per gram of heavy oil, on a total elemental basis of nickel, vanadiumand iron. In other aspects, the heavy hydrocarbon feed can contain atleast about 500 wppm of nickel, vanadium, and iron, such as at leastabout 1000 wppm.

Heteroatoms such as nitrogen and sulfur are typically found in heavyhydrocarbon feeds, often in organically-bound form. Nitrogen content canrange from about 0.1 wt % to about 3.0 wt % elemental nitrogen, or 1.0wt % to 3.0 wt %, or 0.1 wt % to 1.0 wt %, based on total weight of theheavy hydrocarbon feed. The nitrogen containing compounds can be presentas basic or non-basic nitrogen species. Examples of basic nitrogenspecies include quinolines and substituted quinolines. Examples ofnon-basic nitrogen species include carbazoles and substitutedcarbazoles.

The invention is particularly suited to treating heavy oil feedstockscontaining at least 0.1 wt % sulfur, based on total weight of the heavyhydrocarbon feed. Generally, the sulfur content can range from 0.1 wt %to 10 wt % elemental sulfur, or 1.0 wt % to 10 wt %, or 0.1 wt % to 5.0wt %, based on total weight of the heavy hydrocarbon feed. Sulfur willusually be present as organically bound sulfur. Examples of such sulfurcompounds include the class of heterocyclic sulfur compounds such asthiophenes, tetrahydrothiophenes, benzothiophenes and their higherhomologs and analogs. Other organically bound sulfur compounds includealiphatic, naphthenic, and aromatic mercaptans, sulfides, and di- andpolysulfides.

Heavy hydrocarbon feeds can be high in n-heptane asphaltenes. In someaspects, the heavy hydrocarbon feed can contain 1 wt % to 80 wt % ofn-heptane asphaltenes, or 5 wt % to 80 wt % of n-heptane asphaltenes, or5 wt % to 60 wt %, or 5 wt % to 50 wt %, or 20 wt % to 80 wt %, or 10 wt% to 50 wt %, or 20 wt % to 60 wt %. In aspects where the heavyhydrocarbon feed includes a portion of a bitumen formed by conventionalparaffinic froth treatment of oil sands, the heavy hydrocarbon feed cancontain 10 wt % to 30 wt % of asphaltenes.

Still another method for characterizing a heavy hydrocarbon feed isbased on the Conradson carbon residue of the feedstock, or alternativelythe micro carbon residue content. The Conradson carbon residue/microcarbon residue content of the feedstock can be 5.0 wt % to 50 wt %, or5.0 wt % to 30 wt %, or 10 wt % to 40 wt %, or 20 wt % to 50 wt %.

Slurry Hydroconversion Reaction Conditions

In various aspects, a slurry hydroprocessing reactor (or other slurryhydroprocessing reaction system) can be operated using pitch recycle toprovide improved reactor productivity while achieving conversion of lessthan 90 wt % (relative to 524° C) of a heavy hydrocarbon feed, such as60 wt % to 89 wt % conversion, or 70 wt % conversion to 89 wt %conversion. The pitch recycle can correspond to 50 wt % or more of theamount of fresh feed entering the reactor (or reaction system). Forexample, the pitch recycle stream can correspond to 50 wt % to 250 wt %of the amount of fresh feed, or 50 wt % to 200 wt %, or 60 wt % to 250wt %, or 60 wt % to 200 wt %, or 100 wt % to 250 wt %, or 75 wt % to 200wt %. Such amounts for the pitch recycle stream correspond to a combinedfeed ratio of 1.5 to 3.5, or 1.5 to 3.0, or 1.6 to 3.5, or 1.6 to 3.0,or 2.0 to 3.5, or 1.75 to 3.0. The pitch recycle stream can include morethan 50 wt % of 566° C+ components, or 60 wt % or more, such asincluding substantially only 566° C+ components. Optionally, the pitchrecycle stream can include 50 wt % or more of 593° C+ components, or 60wt % or more, such as including substantially only 566° C+ components.

It has been discovered that operating with substantial pitch recycle canprovide a variety of unexpected advantages when performing slurryhydroconversion on a heavy hydrocarbon feed. Such advantages caninclude, but are not limited to, increased reactor productivity andreducing or minimizing reactor fouling. Conventionally, it is believedthat avoiding coke formation and/or fouling required reducing theconcentration of 566° C+ components when using recycle streams; removingasphaltenes from any recycle streams; or a combination thereof.

In particular, recycling pitch can unexpectedly improve reactorproductivity, allowing an increase in the unit capacity at constant 524°C net conversion. This is in contrast to conventional recycle methods,where using recycle streams containing 50 wt % or more of lower boilingcomponents results in loss of reactor productivity (i.e., the fresh feedrate is reduced at constant temperature). For example, when operatingslurry hydroconversion with pitch recycle, the amount of net conversionrelative to 524° C can be 60 wt % to 89 wt %, or 70 wt % to 89 wt %, or60 wt % to 85 wt %, or 70 wt % to 85 wt %, or 75 wt % to 89 wt %. It isnoted that the conversion at 566° C. will be higher than the conversionat 524° C. The per-pass conversion can be lower, corresponding to 60 wt% or less conversion relative to 524° C.

A goal of processing a feed under slurry hydroconversion conditions canbe to convert the refractory 1050° F+ (566° C+) material which cannot bereadily converted in other types of refinery processing units. In suchaspects, it is therefore desirable to maximize the residence time of566° C+ material in the reactor. To increase the 566° C+ residence time,one option can be to first distill the feed to a slurry hydroprocessingreactor to remove 566° C− material. However, even after removal of 566°C− material from the feed, a significant portion of the reactor volumeis occupied by gas and/or conversion products during once-throughoperation. Specifically, a substantial amount of conversion of vacuumgas oil boiling range components can occur during operation at aper-pass conversion of 60 wt % or more relative to 524° C. Secondarycracking (conversion of VGO into distillate, naphtha, and gas rangemolecules) is undesirable since this material could be more economicallyprocessed in other refinery units such as a fixed-bed hydrocracker orfluid catalytic cracker. Such secondary cracking is particularlyundesirable when partially upgrading heavy hydrocarbons, such asbitumen, into synthetic crude oils which are intended to be furtherprocessed in conventional refinery units elsewhere. Additionally, thesecondary cracking results in an increased amount of gas phase materialwithin the slurry hydroconversion reaction environment. Secondarycracking also results in increased light-ends make, with a correspondingundesirable increase in hydrogen consumption.

One alternative for reducing secondary cracking can be to increase thetreat gas rate to strip more 566° C− material from the reactor liquid.Unfortunately, increasing the gas superficial velocity will alsoincrease gas holdup at a fixed liquid superficial velocity, reducingliquid residence time and increasing the potential for foaming However,for a variety of reasons (such as limitations on reactor size or desireto avoid replacing existing equipment), increasing the treat gas rate istypically not a viable method to economically reduce secondary crackingin a slurry hydroconversion system.

High pitch recycle provides an alternative and economical method todecrease secondary cracking. Without being bound by any particulartheory, pitch recycle increases the concentration of 566° C+ material inthe reactor and allows a substantial portion of the pitch molecules tomake multiple passes while conversion products are typically removedafter a single pass. Moreover, per-pass liquid residence time isreduced, further reducing secondary cracking. As a result, the effectiveresidence time of 566° C+ material in the reactor is increased and theeffective residence time of 566° C− material is decreased. It has beendiscovered that his combination of increasing 566° C+ material residencetime while decreasing 566° C− material residence time results in anincrease in primary cracking while suppressing secondary cracking. Theincrease in primary cracking enables increased 566° C+ conversion atfixed reactor volume and fresh feed rate, increased fresh feed rate atfixed conversion and reactor volume, or decreased reactor volume at afixed conversion and fresh feed rate.

Based on the above, from a reactor productivity perspective, it isdesirable to increase or maximize the pitch recycle rate. As thecombined feed rate (defined as mass ratio of fresh feed+recycle dividedby fresh feed) increases, the reactor efficiency increases. The optimalpitch recycle rate can be determined by balancing the benefits of higherreactor efficiency against cost, product yield/quality, hydrodynamic,and reactor stability considerations.

The relative effectiveness of pitch recycle is also a function of the566° C+ content in the recycle stream. At a constant total recycle rate,it has been discovered increasing the concentration of 566° C+ materialin the recycle stream further increases reactor efficiency. Conversely,it has been discovered that if the recycle stream contains too little566° C+ material, pitch recycle will decrease reactor efficiency, asthis reduces the effective residence time of the 566° C+ material. Inorder to achieve improved reactor efficiency, the 566° C+ components ina recycle stream can correspond to more than 50 wt % of the recyclestream, or 60 wt % or more, or 75 wt % or more, such as up to havingsubstantially all of the recycle stream correspond to 566° C+ material.Optionally, 50 wt % or more of the recycle stream can correspond to 593° C+ components, or 60 wt % or more, or 75 wt % or more, such as up tohaving substantially all of the recycle stream correspond to 593° C+material.

In general, pitch recycle results in a heavier product yield slate as650° F− (343° C−) yields are reduced compared to operation withoutsubstantial pitch recycle. Thus, pitch recycle provides a means toincrease the vacuum gas oil yield from processing of a heavy hydrocarbonfeed. Increasing the yield of vacuum gas oil is desirable, since it ismore economical to convert vacuum gas oil material in an alternativeprocess unit such as a fixed-bed hydrocracker or fluid catalyticcracker. Moreover, the naphtha and distillate produced by slurryhydroconversion is typically high in heteroatoms and aromatics comparedto virgin material. As a result, hydroconverted naphtha andhydroconverted distillate fractions from slurry hydroconversiontypically require additional processing to meet finished productspecifications. Therefore, it can be desirable to reduce the yields ofthese products to lower levels such that they can be blended into therefinery mogas/distillate pools without additional processing. Pitchrecycle also reduces the yield of low-value light ends andcorrespondingly lowers hydrogen consumption, further improving processeconomics. As the pitch recycle rate increases, the yield slate willbecome heavier at constant conversion.

The yields at a given recycle rate can also be shifted by adjusting theamount of 1050° F+ (566° C+) material in the recycle stream. In general,increasing the 566° C+ content of the recycle stream will result in aheavier yield slate, while decreasing the 566° C+ content of the recyclestream will result in a lighter yield slate.

The choice of recycle cut point can also impact the quality of the VGO.Recycle operation with deep vacuum distillation shifts the T50 boilingpoint of the VGO product higher, and pulls a significant quantity of566° C+ molecules into the liquid product that includes the VGO. Theseinclude very low hydrogen content polynuclear aromatics. In someaspects, the net result from the above combination of factors is aliquid product from slurry hydroconversion where the 343° C-454° Cboiling range fraction is higher quality and the 454° C+ boiling rangefraction is lower quality (due to the presence of 566° C+ components).

In some aspects, one of the operating challenges for slurryhydroconversion is reducing or minimizing the formation of incompatiblematerial in the reactor. Such incompatible material can deposit in thereactor, reducing the effective reactor volume, or can cause plugging inthe separation/fractionation train, resulting in a unit shutdown. Someincompatible material (coke) is formed during normal operation but iscontrolled by operating at an appropriate hydrogen partial pressure andcatalyst make-up rate.

Operation of a slurry hydroprocessing reactor with pitch recycle returnsincompatible material to the reactor which could result in fouling.However, without being bound by any particular theory, it is believedthat when pitch recycle is performed as described herein, the pitchrecycle can unexpectedly improve the stability of slurry hydrocrackingreactors by increasing the solvency (aromaticity) of the circulatingfeedstocks in the reactor and the distillate products. Additionally oralternately, secondary cracking of primary VGO products intoincompatible paraffin side chains and aromatic cores can be reduced orminimized. Additionally, it has been discovered that the composition ofrecycle pitch has a surprisingly low average molecular weight and thatthe viscosity of the recycle pitch drops unusually quickly astemperature rises. Pitch recycle surprisingly enables high severityslurry hydrocracking without fouling. High temperature operation ofslurry hydroconversion at 800° F to 875° F (427° C to 468° C), orpreferably at 840° F to 860° F (449° C to 460° C) produces a lowviscosity, high aromatic content, high nitrogen recycle fluid thatprevents reactor coking and fouling.

Tailoring the cut point and composition of the recycle stream can alsobe beneficial for remaining within the solubility limit of the reactorliquid. In some aspects, operability of the slurry hydrocracker withpitch recycle is improved by removing low solvency material from thefeed. This can be achieved by, for example, deasphalting atmospheric orvacuum residue to produce a high solvency asphaltene fraction and/or bydeep distillation of atmospheric residue to yield a high solvency vacuumresidue, such as distillation at a cut point of 1050° F (566° C) ormore, or 1080° F (582° C) or more, or 1100° F (593° C) or more.

The slurry hydroconversion process uses a dispersed catalyst which iscontinuously doped into the feed. This catalyst helps to suppress cokeformation by capping free radicals formed by thermal conversion.Measurements of reactor liquid catalyst concentrations indicate thecatalyst tracks the liquid phase. Therefore, when the slurryhydroconversion unit is operated once-through, the catalyst lifetime isequal to the liquid residence time. This is economical because a verylow concentration of catalyst is used and the catalyst cost is low.However, it is desirable to increase the lifetime of the catalyst inorder to reduce catalyst usage. Since it is difficult to isolate thecatalyst from the product, this is most easily accomplished by bottomsrecycle. Bottoms recycle increases the average catalyst lifetime. As aresult, at constant make-up, the concentration of catalyst in thereactor liquid increases as bottoms recycle increases, even afteraccounting for reduced vaporization in the reactor. This allows thecatalyst make-up rate to be reduced while maintaining equivalent cokesuppression activity or, alternatively, the reactor severity can beincreased while maintaining constant coke make. It is noted that inaspects where the heavy hydrocarbon feedstock corresponds to a bitumenderived from a froth treatment, clay particles remaining in the bitumenafter the froth treatment can also contribute catalytic effect. Suchclay particles can also be concentrated by the pitch recycle.

In a reaction system, slurry hydroprocessing can be performed byprocessing a feed in one or more slurry hydroprocessing reactors. Insome aspects, the slurry hydroprocessing can be performed in a singlereactor, or in a group of parallel single reactors. The reactionconditions in a slurry hydroconversion reactor can vary based on thenature of the catalyst, the nature of the feed, the desired products,and/or the desired amount of conversion.

With regard to catalyst, several options are available. In some aspects,the catalyst can correspond to one or more catalytically active metalsin particulate form and/or supported on particles. In other aspects, thecatalyst can correspond to particulates that are retained within theheavy hydrocarbon feed after using a froth treatment to form the feed.In still other aspects, a mixture of catalytically active metals andparticulates retained in the heavy hydrocarbon feed can be used.

In aspects where a catalytically active metal is used as the catalyst,suitable catalyst concentrations can range from about 50 wppm to about50,000 wppm (or roughly 5.0 wt %), depending on the nature of thecatalyst. Catalyst can be incorporated into a hydrocarbon feedstockdirectly, or the catalyst can be incorporated into a side or slip streamof feed and then combined with the main flow of feedstock. Still anotheroption is to form catalyst in-situ by introducing a catalyst precursorinto a feed (or a side/slip stream of feed) and forming catalyst by asubsequent reaction.

Catalytically active metals for use in slurryhydroprocessing/hydroconversion can include those from Groups 4-10 ofthe IUPAC Periodic Table. Examples of suitable metals include iron,nickel, molybdenum, vanadium, tungsten, cobalt, ruthenium, and mixturesthereof. The catalytically active metal may be present as a solidparticulate in elemental form or as an organic compound or an inorganiccompound such as a sulfide or other ionic compound. Metal or metalcompound nanoaggregates may also be used to form the solid particulates.

A catalyst in the form of a solid particulate is generally a compound ofa catalytically active metal, or a metal in elemental form, either aloneor supported on a refractory material such as an inorganic metal oxide(e.g., alumina, silica, titania, zirconia, and mixtures thereof). Othersuitable refractory materials can include carbon, coal, and clays.Zeolites and non-zeolitic molecular sieves are also useful as solidsupports. One advantage of using a support is its ability to act as a“coke getter” or adsorbent of asphaltene precursors that might otherwiselead to fouling of process equipment.

In some aspects, it can be desirable to form catalyst for slurryhydroprocessing in situ, such as forming catalyst from a metal sulfatecatalyst precursor or another type of catalyst precursor that decomposesor reacts in the hydroconversion reaction zone environment, or in apretreatment step, to form a desired, well-dispersed and catalyticallyactive solid particulate. Precursors also include oil-solubleorganometallic compounds containing the catalytically active metal ofinterest that thermally decompose to form the solid particulate havingcatalytic activity. Other suitable precursors include metal oxides thatmay be converted to catalytically active (or more catalytically active)compounds such as metal sulfides.

The slurry hydroprocessing stage can be operated at a net conversion of60 wt % to 89 wt %, relative to a conversion temperature of 524° C, or70 wt % to 89 wt %, or 60 wt % to 85 wt %, or 70 wt % to 85 wt %, or 75wt % to 89 wt %. Optionally but preferably, the slurry hydroprocessingstage can correspond to a single slurry hydroprocessing reactor, asopposed to having a plurality of reactors arranged in series. In someaspects, a portion of the pitch or unconverted bottoms from the slurryhydroprocessing reactor can be recycled. In such aspects, the per-passconversion can be significantly lower, such as having a per-passconversion of 60 wt % or less, or 50 wt % or less, or 40 wt % or less,relative to 524° C or alternatively relative to 566° C.

In addition to operating at reduced conversion, the slurryhydroprocessing reactor can also perform a relatively low level ofhydrodesulfurization and/or hydrodenitrogenation. In various aspects,the amount of nitrogen removal (conversion to NH₃ or other light endnitrogen compounds) can correspond to 35 wt % or less of the organicnitrogen in the feed to the slurry hydroprocessing reactor, or 30 wt %or less, or 25 wt % or less, such as down to 10 wt % or possibly stilllower. Additionally or alternately, the amount of sulfur removal(conversion to H₂S or other light end sulfur compounds) can correspondto 90 wt % or less of the sulfur in the feed to the slurryhydroprocessing reactor, or 85 wt % or less, or 80 wt % or less, such asdown to 60 wt % or possibly still lower. For example, the amount ofsulfur removal can correspond to 60 wt % to 90 wt %, or 70 wt % to 85 wt%.

The reaction conditions within a slurry hydroprocessing reactor thatcorrespond to a target conversion level can include a temperature of400° C to 480° C, such as 425° C or more, or 450° C or more. Some typesof slurry hydroprocessing reactors are operated under high hydrogenpartial pressure conditions, such as having a hydrogen partial pressureof 1000 psig (6.39 MPag) to 3400 psig (23.4 MPag), for example at least1200 psig (8.3 MPag), or at least about 1500 psig (10.3 MPag). Examplesof hydrogen partial pressures can be 1000 psig (6.9 MPag) to 3000 psig(20.7 MPag), or 1000 psig (8.3 MPag) to 2500 psig (17.2 MPag), or 1500psig (10.3 MPag) to 3400 psig (23.4 MPag), or 1000 psig (6.9 MPag) to2000 psig (13.8 MPag), or 1200 psig (8.3 MPag) to 2500 psig (17.2 MPag).Since the catalyst is in slurry form within the feedstock, the spacevelocity for a slurry hydroconversion reaction conditions can becharacterized based on the volume of feed processed relative to thevolume of the reactor used for processing the feed. Suitable liquidhourly space velocities (LHSV) for slurry hydroconversion can range, forexample, from about 0.05 v/v/hr⁻¹ to about 5 v/v/hr⁻¹, such as about 0.1v/v/hr⁻¹ to about 2 v/v/hr⁻¹.

In some aspects, the quality of the hydrogen stream used for slurryhydroprocessing can be relatively low. For example, in aspects where thecatalyst is concentrated into the pitch and removed from the system aspart of a product from a partial oxidation reactor, catalyst lifetimecan be of minimal concern. This is due to the constant addition of freshcatalyst, whether in the form of particulates from the heavy hydrocarbonfeed or in the form of a separately added catalyst. As a result,reaction conditions that conventionally are considered undesirable forhydroprocessing due to catalyst deactivation can potentially be used.This can potentially provide unexpected synergies when a partialoxidation reactor is used to provide at least a portion of the hydrogenfor the hydroconversion process.

One example of a reaction condition that is avoided in conventionalhydroprocessing is use of hydrogen streams that have relatively highconcentrations of known catalyst poisons. Some catalyst poisons cancorrespond to catalyst poisons commonly found in recycled hydrogen treatgas streams, such as H₂S, NH₃, CO, and other contaminants. Othercatalyst poisons can correspond to contaminants that may be present inhydrogen derived from processing of pitch in a partial oxidationreactor, such as nitrogen oxides (NOx), sulfur oxides (SOx), arseniccompounds, and/or boron compounds. In order to use hydrogen generated bypartial oxidation of pitch in a conventional hydroprocessing reactor,various cleanup processes would be needed to reduce or minimize thecontent of various contaminants in the hydrogen treat gas. However,using a partial oxidation reactor to provide hydrogen for a slurryhydroprocessing reactor can provide the unexpected synergy of allowingat least some cleanup steps to be avoided, due to the tolerance of theslurry hydroprocessing reaction conditions for the presence of variouscontaminants.

In some aspects, the H₂ content of the hydrogen-containing streamintroduced into the slurry hydroprocessing reactor can be 90 vol % orless, or 80 vol % or less, or 60 vol % or less, such as down to 40 vol %or possibly still lower. In other aspects, the H₂ content of thehydrogen-containing stream can be 80 vol % or more, or 90 vol % or more.For example, the hydrogen-containing stream can contain 80 vol % to 100vol % H₂, or 90 vol % to 100 vol %, or 80 vol % to 98 vol %, or 90 vol %to 98 vol %, or 80 vol % to 96 vol %, or 90 vol % to 96 vol %.Additionally or alternately, the combined content of H₂S, CO, and NH₃ inthe hydrogen-containing stream can be 1.0 vol % or more, or 3.0 vol % ormore, or 5.0 vol % or more, such as up to 15 vol % or possibly stillhigher. Further additionally or alternately, the combined content of H₂,H₂O, and N₂ in the hydrogen-containing stream introduced into the slurryhydroprocessing reactor can be 95 vol % or less, or 90 vol % or less, or85 vol % or less, such as down to 75 vol % or possibly still lower. Forexample, the combined content of H₂, H₂O, and N₂ in thehydrogen-containing stream introduced into the slurry hydroprocessingreactor can be 75 vol % to 95 vol %.

Example of Slurry Hydroprocessing Reaction System

FIG. 1 shows an example of a slurry hydroprocessing reactor. In FIG. 1,a feed 405 is mixed with at least one of fresh slurry hydrotreatingcatalyst 402 and hydrogen 401 prior to being introduced into slurryhydroprocessing reactor 410. Optionally, a catalyst precursor (notshown) can be added to feed 405 in place of at least a portion of slurryhydrotreating catalyst 402. Optionally, hydrogen stream 401 and/orslurry hydrotreating catalyst 402 can be introduced into the slurryhydroprocessing reactor 410 separately from feed 405. In theconfiguration shown in FIG. 1, pitch recycle stream 465 is combined withfeed 405 prior to passing into slurry hydroprocessing reactor 410. Inother aspects, pitch recycle stream 465 and feed 405 can be passedseparately into slurry hydroprocessing reactor 410.

After exposing the feed to slurry hydroconversion conditions in slurryhydroprocessing reactor 410, the resulting slurry hydroprocessingeffluent 415 can be passed into one or more separation stages. In theexample shown in FIG. 1, the separation stages include a first separator420 and a second separator 430. The first separator performs a highpressure vapor-liquid separation. The vapor fraction 422 corresponds tolight gases and at least part of the reaction products. The liquidfraction 425 corresponds to a combination of vacuum gas oil and pitch.The liquid fraction 425 is passed into second separator 430, where thepitch fraction 465 for recycle is separated from a second productfraction 432. Second separator 430 can correspond to any convenient typeof separator suitable for forming a pitch fraction, such as a vacuumdistillation tower or a flash separator. A pitch removal stream 437 canalso be formed, to remove a portion of the unconverted pitch from therecycle loop. The pitch fraction 465 can be passed into pitch recyclepump 463 prior to being combined with feed 405 and/or separatelyintroduced into reactor 410.

Both vapor fraction 422 and second product fraction 432 can optionallyundergo further separations and/or additional processing, as desired.For example, as shown in FIG. 1, the vapor fraction 422 can be passedinto a subsequent hydrotreating or stabilizer stage 450 to form ahydrotreated vapor fraction 452. In some aspects, the light gases invapor fraction 422 can include sufficient hydrogen for performing thesubsequent hydrotreating 450. The subsequent hydrotreating can be usedto reduce olefin content, reduce heteroatom content (such as nitrogenand/or sulfur), or a combination thereof. In the example shown in FIG.1, the vapor fraction 422 (e.g., naphtha and distillate boiling rangeportions of hydroconversion effluent) is passed into hydrotreating stage450 to form a hydrotreated or stabilized effluent 452. In such aspects,the second product fraction 432 of the hydroconversion effluent,including at least a portion of the vacuum gas oil, can bypass thehydrotreating stage 450. In other aspects, both the vapor fraction 422and the second product fraction 432 can be passed into hydrotreatingstage 450. Optionally, the hydrotreater/stabilizer can be integratedwith the hydroconversion stage. For example, an initial separator can beused to separate the hydroconverted effluent into a lighter portion anda heavier portion that includes the bottoms. Such a separation can beperformed at substantially the exit pressure of the hydroconversionstage. Additionally, any hydrogen in the gas exiting with the effluentcan travel with the lighter portion. In some aspects, the hydrogenexiting with the lighter portion of the effluent can be sufficient toprovide substantially all of the hydrogen treat gas that is needed forperforming hydrotreating the hydrotreating stage 450. The lighterportion (plus hydrogen) can then be passed into the stabilizer withoutrequiring re-pressurization. In other aspects, additional hydrogen canbe provided to the hydrotreating stage 450, such as hydrogen generatedfrom partial oxidation of pitch and/or hydrogen from another convenientsource.

In the configuration shown in FIG. 1, a pumparound recirculation loop isalso shown. In the pumparound recirculation loop, a pumparound portion446 of liquid fraction 425 is passed into pumparound pump 443 prior topassing the pumparound portion 446 into slurry hydroprocessing reactor410.

Comparative Example 1—Fixed Bed Hydroprocessing of Vacuum Resid

A vaccum resid fraction was hydroprocessed in a fixed bed reactor todetermine the impact of recycle on reactor productivity. FIG. 2 showsresults from the hydroprocessing. In FIG. 2, the net conversion of thefeed relative to 1020° F (549° C) is shown relative to the residencetime of fresh feed into the reactor. It is noted that the units for thehorizontal axis are effectively the inverse of a weight hourly spacevelocity. The “circle” data points correspond to once-through operationof the fixed bed reactor, while the “triangle” data points correspond tovarious amounts of recycle of unconverted bottoms back to the fixed bedreactor.

As shown in FIG. 2, hydroprocessing of the vacuum resid feed underonce-through operating conditions versus operating conditions withrecycle had basically no impact on the reactor productivity. This isdemonstrated by the dotted trend line in FIG. 2, which corresponds to astraight line. The fact that the trend line passes through both theonce-through data points and the recycle data points indicates that therelationship between feed residence time and feed conversion was notchanged by use of recycle.

Example 2—Slurry Hydroconversion with Pitch Recycle

A pilot scale configuration similar to the configuration in FIG. 1 wasused to perform slurry hydroconversion on a heavy hydrocarbon feed withvarious types and amounts of recycle. The slurry hydroprocessing reactorwas operated at a feed inlet temperature of 825° F (˜440° C), a pressureof 2500 psig (˜17.2 MPa-g), and an H₂ treat gas ratio of 6000 scf/b(˜1000 Nm³/m³). The fresh feed space velocity was adjusted to maintainnet conversion at roughly 90 wt % relative to 566° C. This was estimatedto correspond to 89 wt % or less conversion relative to 524° C.

The heavy hydrocarbon feedstock was a 975° F+ (524° C+) vacuum residue.The heavy hydrocarbon feedstock included more than 75 wt % of 566° C+components. The pilot plant included a pump-around loop that wasoperated with sufficient recirculation to reduce or minimize foaming Inthe first reaction condition, a recycle stream was used thatcorresponded to 10 wt % of the fresh feed amount. In the second reactioncondition, a recycle stream was used that corresponded to 50 wt % of thefresh feed amount. In the third reaction condition, the recycle streamcorresponded to 100 wt % of the fresh feed amount (i.e., the mass flowrate of the recycle stream was substantially the same as the mass flowrate of the fresh feed). Table 1 provides additional details for eachreaction condition, including the fresh feed rate that was needed tomaintain conversion at roughly 90 wt % relative to 1050° F (566° C)based on the selected reaction temperature, pressure, and H₂ treat gasrate. Table 1 also provides the relative reactor productivity for eachcondition, as well as a 566° C+ conversion rate constant.

TABLE 1 Recycle Conditions Condition 1 2 3 CFR 1.1 1.5 2.0 566° C. + inrecycle, wt % 38 69 64 566° C. + conversion, wt % 91 90 89 (estimated)524° C. + 90 89 89 conversion, wt % Fresh Feed LHSV, hr⁻¹ 0.26 0.36 0.41Reactor Productivity 100 130 140

As shown in Table 1, Condition 1 corresponded to a conventional recycle,where a small recycle stream (˜10% of the fresh feed mass flow rate)containing less than 50 wt % 566° C+ components was used for recycle. Itis believed that the reactor productivity for Condition 1 is similar towhat the reactor productivity would be without recycle. Conditions 2 and3 corresponded to pitch recycle as described herein, where the amount ofthe recycle was 50% or more of the mass flow rate of the fresh feed, andthe recycle stream included greater than 60 wt % 566° C+ components. Asshown in Table 1, operating with a substantial pitch recycle inConditions 2 and 3 allowed for an increase in the fresh feed flow ratefrom 0.26 hr⁻¹ (for 10% recycle) to either 0.36 hr⁻¹ (for 50% recycle)or 0.41 hr⁻¹ (for 100% recycle) while maintaining substantially constantconversion within the slurry hydroprocessing reactor. Thus, operatingwith substantial pitch recycle provided an unexpected productivityincrease. This is in contrast to use of bottoms recycle when performingconversion in a fixed bed environment, where the bottoms recycle hadsubstantially no impact on reactor productivity.

Table 2 shows the product yields from processing the heavy hydrocarbonfeed at each condition. As shown in Table 2, even though Conditions 2and 3 provided an unexpected productivity increase at constantconversion, the amount of hydrogen consumed unexpectedly decreased. Thisunexpected decrease appears to be due in part to reduced production oflight ends and naphtha, with a corresponding increase in vacuum gas oilin the products. The reduction in light ends production also resulted ina net increase in liquid products (C₅-566° C) at Conditions 2 and 3. Forthe product fraction weight percentages in Table 2, the weightpercentages are relative to the weight (i.e., mass flow rate) of thefresh feed.

TABLE 2 Product Yields by Weight (Relative to Fresh Feed) Condition 1 23 H₂ Consumption, scf/b 2200 1900 1770 C₁-C₄, wt % 13.5 9.7 8.6 C₅-177°C., wt % 18.2 15.2 13.4 177° C.-343° C., wt % 33.5 30.4 31.0 343°C.-566° C., wt % 24.9 33.8 35.7 =>VGO API Gravity 11.3 13.6 13.6 =>VGO Ncontent (wt %) 0.762 0.664 0.661 Toluene Soluble 566° C. + wt % 6.7 7.47.8 Toluene Insol 566° C. + wt % 0.6 0.9 0.8 Total C₅-566° C., wt % 76.779.5 80.2

It is noted that pitch recycle also improved the quality of theresulting vacuum gas oil (343° C-566° C), based on an increase in APIgravity and a reduction in nitrogen content. Table 3 providesinformation similar to Table 2, but on a volume basis.

TABLE 3 Product Yields by Volume (Relative to Fresh Feed) Condition 1 23 C₅-177° C., vol % 25.3 20.8 18.5 177° C.-343° C., vol % 40.2 36.4 37.1343° C.-566° C., vol % 25.9 35.6 37.6 Total C₅-566° C., vol % 91.3 92.993.2

Example 3—Product Slate Changes with Pitch Recycle

FIG. 3 and FIG. 4 show model predictions for processing of a heavyhydrocarbon feed with various types of pitch recycle. In FIG. 3, themodeled changes in the resulting product slate from slurryhydroconversion are shown for various amounts of pitch recycle atconstant conversion (relative to 566° C). In FIG. 4, modeled changes inthe product slate from slurry hydroconversion are shown for constantamounts of pitch recycle but with varying amounts of 566° C+ componentsin the recycle stream at constant conversion (relative to 566° C). Asshown in FIG. 3, increasing the amount of pitch recycle resulted in anincrease in the amount of vacuum gas oil in the product slate, with acorresponding decrease in lower boiling products. As shown in FIG. 4,increasing the amount of 566° C+ material in the pitch recycle resultedin an increase in the amount of vacuum gas oil in the product slate,with a corresponding decrease in lower boiling products.

Additional Embodiments

Embodiment 1. A method for performing slurry hydroconversion,comprising: exposing a heavy hydrocarbon feed and a pitch recycle streamto a slurry hydroprocessing catalyst under slurry hydroconversionconditions in a reaction zone to form a slurry hydroprocessing effluent,the slurry hydroconversion conditions comprising a net conversion of 60wt % to 89 wt % relative to 524° C, the heavy hydrocarbon feedcomprising 50 wt % or more of 566° C+ components, the heavy hydrocarbonfeed and the pitch recycle stream comprising a combined feed ratio of1.5 to 3.5; and separating the pitch recycle stream from the slurryhydroconversion effluent, the pitch recycle stream comprising more than50 wt % of 566° C+ components.

Embodiment 2. The method of Embodiment 1, wherein the pitch recyclestream comprises 60 wt % or more of 566° C+ components, or wherein thepitch recycle stream comprises 50 wt % or more of 593° C+ components, ora combination thereof.

Embodiment 3. The method of any of the above embodiments, wherein theheavy hydrocarbon feed comprises 60 wt % or more of 566° C+ components,or wherein the heavy hydrocarbon feed comprises 50 wt % or more of 593°C+ components, or a combination thereof.

Embodiment 4. The method of any of the above embodiments, wherein theheavy hydrocarbon feed comprises 5 wt % to 80 wt % n-heptaneasphaltenes, or wherein the heavy hydrocarbon feed comprises 5 wt % to50 wt % micro carbon residue, or a combination thereof.

Embodiment 5. The method of any of the above embodiments, wherein thecombined feed ratio is 1.6 to 3.0.

Embodiment 6. The method of any of the above embodiments, wherein theslurry hydroconversion conditions comprise 70 wt % to 89 wt % netconversion relative to 524° C.

Embodiment 7. The method of any of the above embodiments, wherein theper-pass conversion at 524° C is lower than the net conversion at 524° Cby 25 wt % or more, or wherein the per-pass conversion at 524° C is 60wt % or less, or a combination thereof.

Embodiment 8. The method of any of the above embodiments, wherein theslurry hydroconversion conditions comprise a temperature of 400° C to480° C, a pressure of 1000 psig (˜6.4 MPa-g) to 3400 psig (˜23.4 MPa-g),and a LHSV of 0.05 hr⁻¹ to 5 hr⁻¹.

Embodiment 9. The method of any of the above embodiments, wherein atleast a portion of the slurry hydroconversion catalyst comprises acatalyst formed in-situ.

Embodiment 10. A slurry hydroconversion effluent made according to anyof Embodiments 1-9.

When numerical lower limits and numerical upper limits are listedherein, ranges from any lower limit to any upper limit are contemplated.While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which the invention pertains.

The present invention has been described above with reference tonumerous embodiments and specific examples. Many variations will suggestthemselves to those skilled in this art in light of the above detaileddescription. All such obvious variations are within the full intendedscope of the appended claims.

1. A method for performing slurry hydroconversion, comprising: exposinga heavy hydrocarbon feed and a pitch recycle stream to a slurryhydroprocessing catalyst under slurry hydroconversion conditions in areaction zone to form a slurry hydroprocessing effluent, the slurryhydroconversion conditions comprising a net conversion of 60 wt % to 89wt % relative to 524° C, the heavy hydrocarbon feed comprising 50 wt %or more of 566° C+ components, the heavy hydrocarbon feed and the pitchrecycle stream comprising a combined feed ratio of 1.5 to 3.5; andseparating the pitch recycle stream from the slurry hydroconversioneffluent, the pitch recycle stream comprising more than 50 wt % of 566°C+ components.
 2. The method of claim 1, wherein the pitch recyclestream comprises 60 wt % or more of 566° C+ components, or wherein thepitch recycle stream comprises 50 wt % or more of 593° C+ components, ora combination thereof.
 3. The method of claim 1, wherein the heavyhydrocarbon feed comprises 60 wt % or more of 566° C+ components, orwherein the heavy hydrocarbon feed comprises 50 wt % or more of 593 ° C+components, or a combination thereof.
 4. The method of claim 1, whereinthe heavy hydrocarbon feed comprises 5 wt % to 80 wt % n-heptaneasphaltenes, or wherein the heavy hydrocarbon feed comprises 5 wt % to50 wt % micro carbon residue, or a combination thereof.
 5. The method ofclaim 1, wherein the combined feed ratio is 1.6 to 3.0.
 6. The method ofclaim 1, wherein the slurry hydroconversion conditions comprise 70 wt %to 89 wt % net conversion relative to 524° C.
 7. The method of claim 1,wherein the per-pass conversion at 524° C is lower than the netconversion at 524° C by 25 wt % or more, or wherein the per-passconversion at 524 ° C is 60 wt % or less, or a combination thereof. 8.The method of claim 1, wherein the slurry hydroconversion conditionscomprise a temperature of 400° C to 480° C, a pressure of 1000 psig(˜6.4 MPa-g) to 3400 psig (−23.4 MPa-g), and a LHSV of 0.05 hr1 to 5hr1.
 9. The method of claim 1, wherein at least a portion of the slurryhydroconversion catalyst comprises a catalyst formed in-situ.
 10. Aslurry hydroconversion effluent made by the method comprising: exposinga heavy hydrocarbon feed and a pitch recycle stream to a slurryhydroprocessing catalyst under slurry hydroconversion conditions in areaction zone to form a slurry hydroprocessing effluent, the slurryhydroconversion conditions comprising a net conversion of 60 wt % to 89wt % relative to 524° C, the heavy hydrocarbon feed comprising 50 wt %or more of 566° C+ components, the heavy hydrocarbon feed and the pitchrecycle stream comprising a combined feed ratio of 1.5 to 3.5; andseparating the pitch recycle stream from the slurry hydroconversioneffluent, the pitch recycle stream comprising more than 50 wt % of 566°C+ components.